The present invention relates generally to tissue and organ stimulating and sensing devices, and more particularly, to a medical adapter for providing connectivity between a cardiac pacer and associated pacer leads and for controlling the operation of the cardiac pacer. The present invention also relates to a medical adapter capable of sending stimulating signals to and receiving sensing signals from a patient""s heart.
Cardiac pacers, which provide stimulation to a patient""s heart, by means of amplitude and frequency modulated electrical pulses, have been developed for permanent or temporary applications. The two most common types of cardiac pacers currently in use are pacemakers and implantable cardioverter-defibrillators (ICD). Cardiac pacers can be implanted in a suitable location inside the patient""s body or located outside the patient""s body. Cardiac pacers operate with one or more conductive leads, which carry stimulating, low voltage electrical pulses, generated by the pacer, to selected sites within the patient""s heart, to communicate sensing signals from those sites back to the cardiac pacer, and to carry high energy pulses, generated by an ICD, to defibrillate the heart, if required.
Furthermore, it is often necessary to provide stimulation of a patient""s heart using a cardiac pacer located outside the patient""s body or to provide temporary stimulation of the patient""s heart.
Such is the case, when a physician might want to try more than one cardiac pacer before selecting the most appropriate one for permanent implantation. To enable the physician to try more than one cardiac pacer before selecting the most appropriate one for permanent implantation, medical cardiac adapters have been developed. These adapters allow a physician to connect various pacers to the patient""s hearts via implanted leads wherein the various pacers may have different interfaces for connecting to the leads. The adapters provide the universal interface between the implanted leads and the pacer so as to provide interchangeability between the pacers. Examples of such previously proposed adapters are disclosed in the following patents.
The Bourney et al. Patent (U.S. Pat. No. 4,545,381) discloses and claims an adapter for converting an implantable cardiac pacer to an externally worn cardiac pacer. This adapter provides a housing to which a cardiac pacer can be secured. It also provides compatibility with a plurality of cardiac pacers.
The Fain et al. Patent (U.S. Pat. No. 5,679,026) discloses and claims a header adapter, which is designed to fit onto the header and case of a cardiac pacer. This header adapter provides a plurality of lead connector configurations, thereby allowing the use of different types of leads and compatibility between leads and cardiac pacers from different manufacturers.
It is also often necessary to maintain proper stimulation of a patient""s heart with an external pacer while the patient is undergoing medical procedures. However, certain medical procedures, such as Magnetic Resonance Imaging (MRI), can interfere with the proper stimulation of a patient""s heart with an external pacer and implanted leads.
MRI is an imaging technique adapted to obtain both images of anatomical features of human patients as well as some aspects of the functional activities of biological tissue. These images have medical diagnostic value in determining the state of the health of the tissue examined.
In an MRI procedure, a patient is typically aligned to place the portion of the patient""s anatomy to be examined in the imaging volume of the MRI apparatus. Such an MRI apparatus typically comprises a primary magnet for supplying a constant magnetic field (B0) which, by convention, is along the z-axis and is substantially homogeneous over the imaging volume and secondary magnets that can provide linear magnetic field gradients along each of three principal Cartesian axes in space (generally x, y, and z, or x1, x2 and x3, respectively). A magnetic field gradient (B0/ xi) refers to the variation of the field along the direction parallel to B0 with respect to each of the three principal Cartesian axes, xi. The apparatus also comprises one or more RF (radio frequency) coils which provide excitation and detection of the MRI signal.
The use of MRI with patients who require medical assist devices, such as external cardiac assist devices or other external medical assist devices that also utilize implanted leads to stimulate a certain tissue region or organ, often presents problems. As is known to those skilled in the art, devices such as pulse generators (IPGs) and cardioverter/defibrillator/pacemakers (CDPs) are sensitive to a variety of forms of electromagnetic interference (EMI) because these enumerated devices include sensing and logic systems that respond to low-level electrical signals emanating from the monitored tissue region of the patient. Since the sensing systems and conductive elements of these devices are responsive to changes in local electromagnetic fields, the devices are vulnerable to external sources of severe electromagnetic noise, and in particular, to electromagnetic fields emitted during the MRI procedure. Thus, patients with such devices are generally advised not to undergo MRI procedures.
To more appreciate the problem, the use of a cardiac assist device during a MRI process will be briefly discussed.
The human heart may suffer from two classes of rhythmic disorders or arrhythmias: bradycardia and tachyarrhythmia. Bradycardia occurs when the heart beats too slowly, and may be treated by a common pacemaker delivering low voltage (about 3 V) pacing pulses having a duration of about 1 millisecond.
The common pacemaker operates in conjunction with one or more electrically conductive leads, adapted to conduct electrical stimulating pulses to sites within the patient""s heart, and to communicate sensed signals from those sites back to the device.
Furthermore, the common pacemaker typically has a metal case and a connector block mounted to the metal case that includes receptacles for leads which may be used for electrical stimulation or which may be used for sensing of physiological signals. Electrical interfaces are employed to connect the leads outside the metal case with the medical device circuitry and the battery inside the metal case.
Electrical interfaces serve the purpose of providing an electrical circuit path extending from the interior of a sealed metal case to an external point outside the case while maintaining the seal of the case. A conductive path is provided through the interface by a conductive pin that is electrically insulated from the case itself.
Such interfaces typically include a ferrule that permits attachment of the interface to the case, the conductive pin, and a hermetic glass or ceramic seal that supports the pin within the ferrule and isolates the pin from the metal case.
A common pacemaker can, under some circumstances, be susceptible to electrical interference such that the desired functionality of the pacemaker is impaired. For example, common pacemaker requires protection against electrical interference from electromagnetic interference (EMI), defibrillation pulses, electrostatic discharge, or other generally large voltages or currents generated by other devices external to the medical device. As noted above, more recently, it has become crucial that cardiac assist systems be protected from intense magnetic and radio frequency (RF) fields associated with MRI.
Such electrical interference can damage the circuitry of the cardiac assist systems or cause interference in the proper operation or functionality of the cardiac assist systems. For example, damage may occur due to high voltages or excessive currents introduced into the cardiac assist system.
Therefore, it is required that such voltages and currents be limited at the input of such cardiac assist systems, e.g., at the interface. Protection from such voltages and currents has typically been provided at the input of a cardiac assist system by the use of one or more zener diodes and one or more filter capacitors.
For example, one or more zener diodes may be connected between the circuitry to be protected, e.g., pacemaker circuitry, and the metal case of the medical device in a manner which grounds current surges through the diode(s). Such zener diodes and capacitors used for such applications may be in the form of discrete components mounted relative to circuitry at the input of a connector block where various leads are connected to the medical device, e.g., at the interfaces for such leads.
However, such protection, provided by zener diodes and capacitors placed at the input of the medical device, increases the congestion of the medical device circuits, requiring at least one zener diode and one capacitor per input/output connection or interface. This is contrary to the desire for increased miniaturization of medical devices.
Further, when such protection is provided, interconnect wire length for connecting such protection circuitry and pins of the interfaces to the medical device circuitry that performs desired functions for the medical device tends to be undesirably long. The excessive wire length may lead to signal loss and undesirable inductive effects. The wire length can also act as an antenna that conducts undesirable electrical interference signals to sensitive ceramic metal oxide semiconductor (CMOS) circuits within the medical device to be protected.
Additionally, the radio frequency (RF) energy that is inductively coupled into the wire causes intense heating along the length of the wire, and at the electrodes that are attached to the heart wall. This heating may be sufficient to ablate the interior surface of the blood vessel through which the wire lead is placed, and may be sufficient to cause scarring at the point where the electrodes contact the heart. A further result of this ablation and scarring is that the sensitive node that the electrode is intended to pace with low voltage signals becomes desensitized, so that pacing the patient""s heart becomes less reliable, and in some cases fails altogether.
A conventional solution for protecting a medical device from electromagnetic interference is illustrated in FIG. 1 that is a schematic view of a medical device 12 embodying protection against electrical interference. At least one lead 14 is connected to the medical device 12 in connector block region 13 using an interface.
In the case where medical device 12 is a pacemaker, the pacemaker 12 includes at least one or both of pacing and sensing implanted leads represented generally as leads 14 to sense electrical signals attendant to the depolarization and repolarization of the heart 16, and to provide pacing pulses for causing depolarization of cardiac tissue in the vicinity of the distal ends thereof.
FIG. 2 more particularly illustrates the circuit that is used conventionally to protect from electromagnetic interference. As shown in FIG. 2, protection circuitry 150 is provided using a diode array component 130. The diode array consists of five zener diode triggered silicon controlled rectifiers (SCRs) with anti-parallel diodes arranged in an array with one common connection. This allows for a small component size despite the large currents that may be carried through the device during defibrillation, e.g., 10 amps. The SCRs 120-124 turn on and limit the voltage across the device when excessive voltage and current surges occur.
As shown in FIG. 2, the zener diode triggered SCRs 120, 121, 123, and 124 are connected to an electrically conductive pin 125, 126, 128, and 129. Further, the electrically conductive pin 125, 126, 128, and 129 are connected to medical device contact regions 131, 132, 134, and 135 to be wire bonded to pads of a printed circuit board. The diode array component 130 is connected to the electrically conductive pins 125, 126, 128, and 129 via the die contact regions along with other electrical conductive traces of the printed circuit board.
As seen above, these conventional approaches fail to provide a method to protect a medical assist device system having implanted leads and using an adapter to coupled the implanted leads to the medical assist device, such as a pacer, during a MRI procedure.
Thus, there is a need to provide an adapter for a cardiac pacing system, which offers a modular approach to connectivity between cardiac pacers and cardiac leads. Moreover, there is a need to provide protection against electromagnetic interference, without requiring much circuitry and to provide fail-safe protection against radiation produced by magnetic resonance imaging (MRI) procedures. Further, there is a need to provide devices that prevent the possible damage that can be done at the tissue interface due to electromagnetic interference or insult. Furthermore, there is a need to provide an effective means for transferring energy from one point of the body to another point without having the energy causing a detrimental effect upon the body.
One aspect of the present invention is a photonic adapter to provide an operational electrical interface between a medical assist device and a photonic catheter. The photonic adapter includes a housing; an electrical interface to provide an operative connection between the photonic adapter and the medical assist device; and a photonic transducer to convert electrical energy from the medical assist device to optical energy, the optical energy being utilized by the photonic catheter.
Another aspect of the present invention is a photonic adapter to provide an operational transmitter/receiver interface between a medical assist device and a photonic catheter. The photonic adapter includes a housing; a transmitter/receiver interface to provide an operative communication connection between the adapter and the medical assist device; and a transducer to convert information from the medical assist device into optical energy.
A third aspect of the present invention is an electromagnetic radiation immune medical assist system. The electromagnetic radiation immune medical assist system includes a medical assist device; a photonic lead having a proximal end and a distal end; and an adapter to operatively connect the medical assist device with the photonic catheter. The adapter includes a housing, an interface to provide an operative communication connection between the adapter and the medical assist device, and a transducer to convert information from the medical assist device into optical energy.
A fourth aspect of the present invention is an adaptive bridge for providing an interface between a photonic adapter and a medical assist device. The adaptive bridge includes a first interface to provide an electrical connection between the adaptive bridge and the medical assist device; a second interface to provide an electrical connection between the adaptive bridge and the photonic adapter; and a passive electrical lead to provide an electrical conduit between the first interface and the second interface.
A fifth aspect of the present invention is a medical assist system. The medical assist system includes a medical assist device; a photonic adapter; and an adaptive bridge for providing an interface between the photonic adapter and the medical assist device.